swap mercruiser 470 to merc 120?!

[karhawk]

Got a real cheap open bow Sea Ray 16' boat with a frozen merc 470 motor, I also got a good running 120-140 merc engine real cheap , aside from the front motor mounts which don't quite line up what other problems am I looking at? I know I will be down on HP, will the exhaust bellows line Up? I have a fix for the front mounts but if the exhaust doesn't line up am I hosed? Got the old engine out and
we are ready to install other motor. What are the obvious differences between the 120 and 140 merc engines?

Thanks
Chris
Oakland, ca

 

[Blujay96]

Re: swap mercruiser 470 to merc 120?!

A 120 is a 2.5 liter and the 140 is a 3.0 liter

 

[Bondo]

Re: swap mercruiser 470 to merc 120?!

What are the obvious differences between the 120 and 140 merc engines?

Ayuh,... The 3.0l has a harmonic balancer,+ pulley...
The 2.5L has only a pulley...

I have no idea if anything will line up,...

Good Luck...

 

[Don S]

Re: swap mercruiser 470 to merc 120?!

aside from the front motor mounts which don't quite line up what other problems am I looking at?

Around 40 less horse power, wrong gear ratio in the outdrive, wrong exhaust tube from transom shield to engine.
If you do find an axhaust tube that will fit, you are still going to have a 10-15 mph boat.

 

[karhawk]

Re: swap mercruiser 470 to merc 120?!

Around 40 less horse power, wrong gear ratio in the outdrive, wrong exhaust tube from transom shield to engine.
If you do find an axhaust tube that will fit, you are still going to have a 10-15 mph boat.

seriously 10-15 mph? I can run faster then that! I'd be willing to bet you on that. as far as the gear ratio, the 120 came with the upper half of the out drive, would that solve the gear problem? This sea ray weighs about 2200 lbs?

Thanks
Chris

 

[karhawk]

Re: swap mercruiser 470 to merc 120?!

I see that 2.5's have a gear ratio of 1.98 and 470's are 1.84 are these ratios the top gear sets on the outdrives? Can you swap just the top half of the outdrive or do you have the change the whole drive to gear rations?

Chris

 

[achris]

Re: swap mercruiser 470 to merc 120?!

I see that 2.5's have a gear ratio of 1.98 and 470's are 1.84 are these ratios the top gear sets on the outdrives? Can you swap just the top half of the outdrive or do you have the change the whole drive to gear rations?

Chris

Top box determines overall drive ratio... so swapping just the top box will change the drive ratio...

Chris...........

 

[karhawk]

Re: swap mercruiser 470 to merc 120?!

thanks
I should use the top half of the merc 120 with the lower half of the 470 to get the better gear ratio they should mate up since the upper and lowers are pre alpha right?

 

[achris]

Re: swap mercruiser 470 to merc 120?!

thanks
I should use the top half of the merc 120 with the lower half of the 470 to get the better gear ratio they should mate up since the upper and lowers are pre alpha right?

right